The present invention relates to insecticidal bait compositions for use against insects having social contact, in particular to bait compositions that exhibit both a primary kill and an effective secondary kill.
Insecticidal bait compositions are generally materials that will be eaten by insects of at least one species and will either directly kill insects, affect the fecundity of the insect so that the insect population is reduced in the next generation, or alter the behaviour of the insect in a manner that will bring about their destruction.
It is usual for bait compositions to contain one or more insecticides in combination with one or more food materials and optionally an attractant. Note that some materials will function both as a food source and as an attractant.
Bait compositions are presented in a variety of forms including tablets, pastes, gels and other semi-solid preparations. Given the toxic nature of the insecticide(s) included in the bait composition, for safety reasons in use they are frequently held in a container or housing that only allows insect access. For this reason, it is important to ensure that baits are sufficiently effective both in delivery of insecticides and attractancy to the insects,
The art is replete with insecticides together with a wide variety of bait compositions. Many of these insecticides are effective providing that they are consumed by insects and therefore in use can bring about a high rate of insect mortality.
Notwithstanding the effectiveness of many insecticides, in order to bring about a substantial reduction in total insect population, it is necessary to maximize the attractiveness of baits so as to maximise the proportion of insect population that will be brought into direct contact with bait compositions.
One can also provide bait compositions which are capable of transmission between insects so as to bring about a greater reduction in insect population. The effectiveness of such compositions is not directly dependent upon each insect consuming the bait composition at its source.
In the art, the extent to which an insect population is reduced by direct contact with the bait composition is referred to as xe2x80x9cprimary killxe2x80x9d. Similarly, the extent to which an insect population is reduced as a result of transmission of bait composition between insects is referred to as xe2x80x9csecondary killxe2x80x9d.
The present inventor has recognised that in the case of insects having social contact such as cockroaches and in the case of social isects such as ants. it is evident that bait compositions exhibiting both effective primary and secondary kills will bring about a greater reduction in insect population than a composition exhibiting a primary kill effectiveness alone.
Surprisingly, the present inventor has found that an insecticidal bait composition exhibiting both effective primary and secondary kills may be achieved through the use of a combination of two insecticides where one insecticide is substantially active as a primary kill agent and a second microencapsulated insecticide is substantially active as a secondary kill agent.
As used in this specification, all concentrations are % w/w unless otherwise specified.
Accordingly, the present invention provides an insecticidal bait composition comprising a solid or semi-solid bait matrix including a food material for an insect and one or more non-microencapsulated insecticides in an amount effective to act essentially as a primary kill agent and one or more microencapsulated insecticides, excluding pyrethroids, in an amount effective to act essentially as a secondary kill agent, the non-microencapsulated insecticide and microencapsulated insecticide being the same or different.
In another aspect, the present invention provides a method of killing insects that have social contact comprising exposing an insect population to an insecticidal bait composition comprising a solid or semi-solid bait matrix including a food material for an insect and one or more non-microencapsulated insecticides in an amount effective to act essentially as a primary kill agent and one or more microencapsulated insecticides, excluding pyrethroids, in an amount effective to act essentially as a secondary kill agent, the non-microencapsulated insecticide and microencapsulated insecticide being the same or different.
In a further aspect, the present invention provides for the use of effective amounts of one or more non-microencapsulated insecticides in combination with one or more microencapsulated insecticides, excluding pyrethroids, ill a solid or semi-solid bait matrix including a food material for an insect, the non-microencapsulated insecticide and microencapsulated insecticide being the same or different and acting respectively essentially as a primary kill agent and a secondary kill agent.
Without wishing to be bound by theory, it is thought that secondary kill occurs as a result of one or more of the following mechanisms:
(a) Faeces of insects that have already consumed a bait include residual insecticide which is ingested by other insects.
(b) Insects that have died as a result of consuming a bait are cannibalised by other insects or perhaps by eating or digesting secretions from the dead or dying insects.
(c) Social contact between insects where particles of bait composition including insecticide are passed.
(d) As a result of preening and insect movement, particles of bait composition are distributed over a surface allowing for insects moving over the surface to subsequently consume the bait particles.
Bait Matrix
The bait matrix will include one or more food materials for the insect. In addition, the bait matrix may comprise a variety of other components including insect attractant(s), fillers and materials as required to prepare the composition in a suitable form.
Amongst the food materials that may be used are: lipids, carbohydrates, proteins, essential oils, water, spices and mixtures thereof. Preferred food materials comprise short chain polysaccharides including starches such as are present in flours, particularly corn flour. Other preferred food materials include fats and oils such as fully hydrogenated fatty acids, preferably fully hydrogenated peanut oil as well as oils such as soy bean oil which also acts as an attractant for cockroaches.
Other fatty materials that may be used include esters, waxes, soaps, phospholipids such as lecithin, glycolipids, turpenes and steroids.
Preferred carbohydrates and protein materials include cereal products such as bran and wheat germ; vegetable products such as potato flour, dehydrated vegetables; sugars, starches and complex carbohydrates including monosaccharides and cellulosic materials; dried yeast, egg powder and insect derived materials such as silkworm pupa, eggs and body parts.
In general terms, the bait matrix may comprise from 85 to 99.9% w/w of the composition. Preferably the bait matrix will be in a concentration of 90 to 99.9% w/w, most preferably 95 to 99.8% w/w.
As noted above, it is desirable to include insect attractant(s) in order to ensure that contact between insect and bait composition is maximised. Amongst the attractants that may be used are pheromones, yeast extracts, complex foods and volatile materials such as flavour essences and food derivatives including fenugreek, herbs and spices.
When insecticides are themselves repellant in nature to insects, preferably an attractant as taught and disclosed in International Patent Application No PCT/AU96/00374 (U.S. 08/665877) now abandoned is used.
Preferably, attractants will be included in the composition in a concentration of 0.01% to 5% w/w.
Desirably, the attractants will also function as food materials. Likewise, it is desirable that the food materials also function as attractants.
As mentioned above, bait compositions generally may be presented in a variety of forms. The bait compositions of this invention may be presented as tablets, pastes, gels and other solid and semi-solid forms. Of these, pastes, gels and semi-solid forms are preferred. Particularly preferred are the semi-solid compositions taught and disclosed in AU-A-9218651, the contents of which are included herein by way of cross reference. The advantage of such compositions is that they are substantially non-crumbling, cohesive and non-particulate in character. This means that when used in a typical bait housing, as taught and disclosed in AU-B-9220748, the composition will not be released into the enviroment. This is particularly important in relation to the safety of children who otherwise may gain access to relatively toxic materials.
Accordingly, compositions that are particulate in character, such as dusts, powders and granules are not suitable forms for the compositions of the invention.
It is also desirable to include a preservative since growth of microorganisms on the composition may function to repel insects. Amongst the preservatives that may be used are sorbic acid and its salts, Dowicil(copyright) (Dow-Elanco) and methyl- and propyl-parabens.
In compositions that include fats and/or oils, it may be appropriate to include an antioxidant such as butylated hydroxytoluene or butylated hydroxyanisole.
Non-micrenicapsulated Insecticide
The one or more non microencapsulated insecticides may be chosen from a wide range of insecticides known in the art including pyrethroids, avermectinis, hydrarnethylnon, fluorinated suifluoramides, organophosphates including diazinon and chlorpyrifos, pyrazoles such as fipronil, carbamates and hydrazones. A preferred insecticide is chlorpyrifos.
The insecticide(s) chosen will generally be incorporated in a concentration of from 0.01 to 5% w/w preferably from 0.02 to 3% w/w, most preferably from 0.04 to 1% w/w.
Microencapsulated Insecticide
The one or more microencapsulated insecticides may be chosen from a wide range of insecticides known in the art, excluding pyrethroids, but including avermectins, hydramethylnon, sulfluoramid, organophosphates including diazinon and chlorpyrifos, carbamates and hydrazones. A preferred insecticide is chlorpyrifos.
A variety of microencapsulation methods and compositions which are well known in the art may be applied to these insecticides. In choosing a microencapsulation composition, it is important to ensure that the composition is compatible with the bait matrix, that is the insecticide is not released into the composition.
A further consideration is that in accordance with the theory of the mechanism by which secondary kill may occur, a further desirable property is that the microencapsulated material has some resistance to digestion by the insect.
Generally, microencapsulated insecticide(s) will be incorporated in a concentration of from 0.01% to 5% w/w, preferably 0.02 % to 3% w/w, most preferably 0.05% to 1.0% w/w, especially 0.05% to 0.5% w/w. Note that these concentrations are with respect to the active insecticide contained in the microcapsules.
The compositions of the invention are effective against social insects, particularly cockroaches and ants, especially cockroaches.
In order to better understand the nature of the invention, an example will now be described: